WO2010105328A1

WO2010105328A1 - Apparatus, systems and methods for mass transfer of gases into liquids

Info

Publication number: WO2010105328A1
Application number: PCT/CA2009/000323
Authority: WO
Inventors: Evan E. Koslow
Original assignee: Koslar Technologies, Llc
Priority date: 2009-03-16
Filing date: 2009-03-16
Publication date: 2010-09-23
Also published as: US20120067427A1

Abstract

An apparatus for mass transfer of a gas into a liquid, including a tank that defines a chamber for receiving the gas, and at least one surface provided within the chamber. Each surface has an inner region, an outer region and an edge adjacent the outer region. Each surface is configured to receive the liquid at the inner region and rotate such that the liquid flows on the surface from the inner region to the outer region, and, upon reaching the edge of the surface, separates to form liquid particles that move outwardly through the gas in the chamber. The liquid particles are sized so that the gas is absorbed by the liquid particles to produce a mixed liquid saturated with the gas during a brief flight time of the liquid particles through the chamber.

Description

Title: Apparatus, Systems and Methods for Mass Transfer Of Gases Into

Liquids

Technical Field

[0001] The embodiments disclosed herein relate to mass transfer, and in particular to apparatus, systems and methods for mass transfer of gases into liquids.

Introduction

[0002] There are numerous industrial processes and types of equipment used to promote the mass transfer of gases into liquids. In many cases, the mass transfer of a gas into a liquid is limited by the mass-transfer resistance at the gas-liquid interface and the diffusion of the gas away from this interface. For example, the binary diffusion coefficient of carbon dioxide in air is 0.139 sq. cm/sec, while the binary diffusion coefficient for carbon dioxide in water is 0.00002 sq. cm/sec.

[0003] Since the diffusivity of a gas within a gas is typically around

1 ,000-10,000 times greater than the diffusivity of a gas into a liquid, dispersion of the liquid is important for effecting mass transfer of a gas into a liquid. For example, if a liquid can be dispersed as droplets having a characteristic droplet length roughly equal to the square root of the binary diffusion coefficient (e.g. for carbon dioxide into water, VO.00002 = 0.0044 cm, or 44 micrometers), then the diffusion will tend to be extraordinarily rapid.

[0004] Generally, to provide for optimum mass transfer rates, all of the liquid should be provided with a similar droplet size having the characteristic diffusion length. Any quantity of liquid that has a larger droplet size will not provide for rapid diffusion, and will not reach equilibrium in the surrounding gas environment within a brief period of time (as is the case with the smaller droplets).

[0005] In many prior art systems, the mass-transfer resistance may be partially overcome by increasing the gas-liquid surface (e.g. by performing mechanical work on the liquid). For example, some systems use powerful mechanical mixers to agitate the liquid. Other systems create small bubbles of gas by pressing a gas through small orifices, and then the bubbles are allowed to rise through a liquid column. However, neither of these approaches is particularly good at overcoming the mass-transfer resistance.

[0006] One technique that would be beneficial is to cause the liquid to be dispersed into the gas, rather than the gas into the liquid. In practice, however, this is very difficult to achieve. Some prior art systems attempt this using high-pressure nozzles to disperse a liquid as fine droplets. Other systems use a two-phase flow of gas and liquid through a nozzle at lower pressure. However, these types of systems are also generally undesirable, as they may require high-pressure, pressure-boosting pumps to be used, or make an undesirable use of gas to disperse the liquid (e.g. using two-phase nozzles). In particular, when attempting a precision transfer of gas into liquid, two-phase nozzles are often unacceptable as the amount of gas required to accomplish the required breakup of the liquid is normally not the quantity of gas that is desired to be transferred into the liquid.

[0007] Accordingly, such systems are not appropriate for many applications, especially where precise control of the ratio of gas to liquid is desired, such as in beverage carbonation (e.g. for soda pop and similar beverages).

[0008] Another technique for dispersing liquid uses violent impaction of the liquid against a set of rotating blades. However, impaction is also undesirable, as the impacted liquid tends to be dispersed as droplets of poly- disperse sizes (e.g. some droplets are quite small while other droplets may be quite a bit larger). As discussed above, the larger droplets will tend not to reach equilibrium along with the smaller droplets, and thus do not provide for good diffusion of the liquid.

[0009] Furthermore, if the time provided for dispersion is extremely brief, then only a portion of the poly-disperse droplets may achieve a target gas content, and this proportion will be a complex function of the integrated gas transferred into the droplets of various sizes. [0010] In the specific case of beverage carbonation (e.g. for soda pop and similar beverages), there are numerous examples of systems involving the mixing of bulk carbon dioxide and water, for example McCann et al. in U.S. Patent 5,855,296; Hancock and May in U.S. Patent 4,850,269; Burrows in U.S. Patents 5,073,312 and 5,071 ,595; Vogal and Goulet in U.S. Patent 5,792,391 ; Goulet in U.S. Patent 5,419,461 ; Notar et al. in U.S. Patent 5,422,045; Bellas and Derby in U.S. Patents 6,935,624 and 6,758,462; Hoover in U.S. Patent 4,745,853; and Singleterry and Larson in U.S. Patent 5,842,600.

[0011] Some example systems include the use of a spinning turbine within a carbonator. For example, U.S. Patent 5,085,810 (Burrows) describes using jets of liquid to drive an impeller that is affixed to an elongated shaft supporting a series of discs that are submerged in a liquid. In this case, the impeller is not driven by a motor, but instead is driven by the force of the incoming liquid, which is used to rotate the shaft (and thus cause the discs attached to the shaft to also rotate). Burrows does not focus on liquid dispersion through impaction, but is instead an effort to eliminate the drive motor normally used to rotate the submerged discs.

[0012] A nearly identical arrangement is described by Koenig and

Erlanger in U.S. Patent 610,062, published in 1898. Again, the incoming liquid is allowed to impinge upon an impeller so as to cause an elongated shaft to rotate, which rotates additional impellers submerged within a body of liquid, causing mixing.

[0013] U.S. Patent 4,804,112 by E.L. Jeans describes a liquid entering a pressurized vessel containing carbon dioxide gas being allowed to impact a bladed rotor. The mechanism of causing the break-up of the liquid into droplets is impaction upon the blades of the rotor. As will be understood by those skilled in the art, impaction involves the turbulent breakup of the liquid, and results in the production of droplets varying widely in size (e.g. droplets with poly-disperse sizes). In addition, the size of the droplets generated by Jeans is generally large (e.g. larger than 75 micrometers) unless - A -

extraordinary impaction velocities are achieved (i.e. velocities approaching the speed of sound in a liquid).

[0014] Any large droplets formed through the use of impaction inhibits achieving gas absorption equilibrium, and hence a significant volume of the liquid in such systems will have insufficient gas saturation. Accordingly, elevated pressure must be used to achieve the target gas content within the liquid under such conditions. However, this creates a potential for exceeding the target saturation, especially if the liquid and gas are left within the carbonation chamber for an extended period of time.

[0015] Accordingly, there is a need in the art for improved apparatus, systems and methods for mass transfer of gases into liquids.

Summary

[0016] In some embodiments described herein, a fine dispersion of liquid is generated using a spinning disc apparatus or a rotating capillary apparatus to generate small liquid particles. The small liquid particles are then dispersed into gas to carry out the mass transfer of the gas into the liquid droplets. The liquid particles may then coalesce with the chamber and/or against the walls of the chamber, and be subsequently collected for extraction.

[0017] Generally, it is desirable that the liquid dispersion produces an exact droplet size, or at least a dispersion of liquid droplets that are almost entirely and reliably below a critical size, so as to closely approach equilibrium with the surrounding gas within extremely brief time scales. In some examples, it would be desirable to perform such dispersion in less than a few seconds, and in some cases within tens of milliseconds.

[0018] The embodiments described herein generally form droplets of uniform or near-uniform size through the use of elegant physics for droplet formation and by balancing forces at the edge of a generally flat spinning disc or within a rotating capillary. In addition, the power consumption for such embodiments tends to be very low. Furthermore, the edge velocities and angular velocities required to achieve essentially complete reduction of the liquid into the required droplet size tend to be quite modest.

[0019] Some embodiments as described herein provide a simple apparatus that tends to produce a uniform and precise dispersion of a liquid into a mist or spray having a specific droplet size and with minimal potential for any significant volume of the liquid being dispersed as over-sized droplets (e.g. droplets that are larger than desired).

[0020] In some examples, this dispersion may be carried out within a space or chamber that operates at elevated pressure so as to cause a gas to rapidly dissolve into the liquid droplets and approach equilibrium saturation during the flight time of the droplets (e.g. between when they are thrown or disengage from the spinning disc and before contacting the walls of the chamber).

[0021] To accomplish the required mass transfer within the brief flight time of the droplets, the droplets generally should be extremely small. Furthermore, the distance between the edge of the spinning disc and the walls of the chamber should be sufficient to allow the droplets to closely approach saturation with the surrounding gas prior to being arrested against the walls. If the droplets are sufficiently small, they will slow and even come to rest before engaging the chamber walls and thus their contact time with the gas can be extended.

[0022] According to one aspect, there is provided an apparatus for mass transfer of gas into a liquid, comprising a tank that defines a chamber for receiving the gas, and at least one surface provided within the chamber, each surface having an inner region, an outer region and an edge adjacent the outer region, wherein each surface is configured to receive the liquid at the inner region and rotate such that the liquid flows on the surface from the inner region to the outer region, and, upon reaching the edge of the surface, separates to form liquid particles that move outwardly through the gas in the chamber, and wherein the liquid particles are sized so that the gas is absorbed by the liquid particles to produce a mixed liquid saturated with the gas during a brief flight time of the liquid particles through the chamber.

[0023] According to another aspect, there is provided a carbonator for mass transfer of carbon dioxide into water, comprising a tank that defines a chamber for receiving the carbon dioxide, and at least one surface provided within the chamber, each surface having an inner region, an outer region and an edge adjacent the outer region, wherein each surface is configured to receive the water at the inner region and rotate such that the water flows on the surface from the inner region to the outer region, and, upon reaching the edge of the surface, separates to form water particles that move outwardly through the carbon dioxide in the chamber, and wherein the water particles are sized so that the carbon dioxide is absorbed by the water particles to produce a carbonated water saturated with the carbon dioxide during a brief flight time of the water particles through the chamber.

[0024] According to yet another aspect, there is provided a method for mass transfer of gas into a liquid, comprising the steps of providing a chamber having the gas therein, providing at least one surface within the chamber, each surface having an inner region, an outer region and an edge adjacent the outer region, providing a liquid to the inner region of each surface, and rotating the surface at an angular velocity selected such that the liquid will move from the inner region to the outer region, and, upon reaching the edge, separates from the at least one surface to form at least one liquid particle that moves outwardly through the gas, wherein the liquid particles are sized so that the gas is absorbed by the liquid particles to produce a mixed liquid saturated with the gas during a brief flight time of the liquid particles through the chamber.

Brief Description of the Drawings

[0025] The drawings included herewith are for illustrating various examples of apparatus, systems and methods of the present specification and are not intended to limit the scope of what is taught in any way. In the drawings: [0026] Figure 1 is a cross-sectional perspective view of an apparatus for mass transfer of a gas into a liquid according to one embodiment;

[0027] Figure 2 is a cross-sectional elevation view of the apparatus of

Figure 1 ;

[0028] Figure 3 is an overhead schematic view of the spinning disc and chamber of the apparatus of Figure 1 ; and

[0029] Figure 4 is a cross sectional elevation view of a rotor assembly for an apparatus for mass transfer of a gas into a liquid according to another embodiment.

Detailed Description

[0030] Illustrated in Figures 1 to 3 is an apparatus 10 for mass transfer of a gas into a liquid according to one embodiment of the invention.

[0031] The apparatus 10 generally includes a tank 12 that defines a chamber 14 into which the gas and liquid may be generally received for effecting the mass transfer.

[0032] The apparatus 10 also generally includes a disc 20 that is provided within the chamber 14. The disc 20 has a surface configured to receive a liquid thereon and can rotate so as to cause a fine dispersion of liquid particles to be ejected from the edges thereof, as will be described in greater detail below.

[0033] The tank 12 may be a pressure vessel or any other suitable vessel, and may be capable of operating at elevated pressures according to the desired operating conditions of the apparatus 10. For instance, in some examples, the tank 12 is configured to operate up to pressures of 3 atmospheres or greater.

[0034] As shown, the tank 12 may include a separate top tank head 16 and bottom tank head 18, each having upper and lower mounting flanges 22, 24 extending outwardly from the perimeter thereof. The mounting flanges 22, 24 may be coupled together using one or more fasteners (e.g. bolts 28, washers 30 and nuts 32) so as to secure the upper tank head 16 and lower tank head 18 together to define the chamber 14 therebetween.

[0035] In some examples, a flange gasket 26 may be provided between the flanges 22, 24 so as to help seal the tank heads 16, 18 together and to inhibit leaks.

[0036] As shown, each of the upper and lower tank heads 16, 18 have outer walls generally located around the perimeter of the chamber 14. For example, the upper tank head 16 has a peripheral upper chamber wall 34, and the lower tank head 18 has a peripheral lower chamber wall 36.

[0037] As shown, the upper tank head 16 has a bulkhead fitting 38 (or liquid inlet fitting). The bulkhead fitting 38 is configured to be coupled to a liquid supply (e.g. using a hose, not shown) so that liquid may be pumped into the chamber 14 during use of the apparatus 10.

[0038] The upper tank head 16 may include an upper puck 40 for securing the bulkhead fitting 38 to the tank head 16. The upper puck 40 may help to stabilize the upper tank head 16 so as to provide for a more secure coupling of the bulkhead fitting 38. In some examples, the bulkhead fitting 38 and upper puck 40 may be welded to the upper tank head 16.

[0039] The bulkhead fitting 38 is coupled to an inlet spout 42 that extends generally downwardly into the chamber 14. The inlet spout 42 is configured to provide liquid to an inner region 20a of the spinning disc 20 during use of the apparatus 10, as will be described in greater detail below.

[0040] The upper tank head 16 also generally includes a gas inlet 44

(shown in Figure 1). The gas inlet 44 is configured to be coupled to a gas supply using a coupling member (e.g. a hose, not shown) for providing gas to the chamber 14 during use of the apparatus 10.

[0041] The lower tank head 18 also generally includes an outlet fitting

46. The outlet fitting 46 is configured to allow extraction of the gas and liquid mixture (e.g. using a hose, not shown) that is generated by the apparatus 10 and which tends to collect in the lower tank head 18 during use. [0042] The apparatus 10 may also include a pH sensor 48, which may be coupled to the lower tank head 18 using a sensor fitting 50. The pH sensor 48 has a sensor tip 52 that extends into the chamber 14 and is configured to measure the pH levels of the gas-liquid mixture that collects in the lower tank head 18.

[0043] Based on the pH levels observed by the pH sensor 48, the properties of the gas-liquid mixture can be monitored and decisions may be made about the operation of the apparatus 10, such as whether additional quantities of liquid and/or gas should be added to the apparatus 10, and/or whether the gas-liquid mixture is ready for extraction via the outlet fitting 46.

[0044] In some examples, the tank 12 also includes a float switch 54 mounted to the lower tank head 18 via a switch fitting 56. The float switch 54 may be configured to monitor the level of the gas-liquid mixture within the lower tank head 18. Based on the height of the mixture, the float switch 54 may be used to trigger extraction 46 of the mixture, control the rate of liquid flowing in through the inlet spout 42, and/or take other actions.

[0045] In particular, the float switch 54 can ensure that the level of mixed liquid in the chamber 14 remains below the surface of the disc 20, so that liquid from the inlet spout 42 does not immediately contact the mixture, but is first dispersed by the disc 20 (as will be described in greater detail below). This also tends to ensure that the mixture does not interfere with the rotation of the disc 20.

[0046] The apparatus also generally includes a drive mechanism 60 configured for rotating or spinning the disc 20 about an axis of rotation A. The drive mechanism 60 may generally be any suitable drive (e.g. a magnetic drive) and may include an inner rotor 62 configured to rotate and an outer rotor 64 that is mechanically coupled to an electric motor or other suitable source of powered rotation. For instance, in this example, the inner and outer rotors 62, 64 are magnetically coupled so that the inner rotor 62 rotates when the outer rotor 64 is caused to rotate. [0047] The inner rotor 62 is generally coupled to a shaft 66 that extends upwardly into the chamber 14. The shaft 66 has an upper portion 66a that is coupled to the disc 20 so that as the inner rotor 62 rotates, the shaft 66 and disc 20 also rotate.

[0048] The shaft 66 may be received within a shaft housing 68 configured to support and stabilize the shaft 66 and disc 20 during rotation. One or more journal bearings 70 may be provided between the shaft 66 and housing 68 so as to inhibit wear during rotation. In some examples, the journal bearings 70 may be plastic, or any other suitable material.

[0049] In some examples, a cap 72 may extend downwardly from the bottom of the lower tank head 18. The cap 72 may house elements of the drive mechanism 60 (e.g. the inner rotor 62 and a lower portion of 66b of the shaft 66) generally below the tank 12, which may facilitate the operation of the drive mechanism 60 (e.g. the magnetic coupling between the inner and outer rotors 62, 64).

[0050] As shown, the cap 72 may be coupled to a lower puck 78 provided in the lower tank head 18 using one or more fasteners 74, and may have a gasket 76 provided between the lower puck 78 and the barrier 72 to assist with inhibiting leaks.

[0051] In some examples, the inner rotor 62 may be coupled to a thrust bearing 80 (which may be plastic or any other suitable material).

[0052] The drive mechanism 60 may be used to rotate the disc 20 at elevated speeds selected according to the desired operating conditions of the apparatus 10. For example, the disc 20 may be rotated at speeds up to and including 3600 RPM. Alternatively, the disc 20 may be rotated at speeds of greater than 3600 RPM.

[0053] In some examples, the tank 12 may also include a safety release valve (not shown) so as to inhibit an overpressure situation from forming within the chamber 14, and which could otherwise damage the components therein and/or cause the tank 12 to crack or burst. [0054] As shown, the disc 20 generally has a flat upper surface (as shown in Figure 1) and has a circular shape, with a disc diameter D (as shown in Figure 3). However, in other examples, the disc 20 may have other shapes (e.g. the surface of the disc 20 may be convex or concave, the disc 20 may not be circular, etc.).

[0055] In some examples, the disc 20 may be made of a metal (e.g. steel, aluminum, etc.). In other examples, this disc 20 may be made of another material that is suitable for rotation at elevated speeds, such as high- strength plastics or ceramics.

[0056] During use of the apparatus 10, liquid (e.g. water) may be fed to the inner region 20a of the disc 20 using the inlet spout 42, and the drive mechanism 60 may be used to rotate the disc 20 about the axis of rotation A.

[0057] As shown, a lower end portion 42a of the inlet spout 42 may be positioned adjacent or directly above the upper surface of the disc 20. Accordingly, the liquid can be directed onto the disc 20 in a generally smooth manner (e.g. without violent impaction that could cause poly-disperse sizes of droplets to be formed).

[0058] The rotation of the disc 20 generally causes the liquid to move from the inner region 20a outwardly towards an outer region 20b of the disc 20. As the liquid moves outwardly, it tends to spread upon the surface of the disc 20, generally forming a thin film.

[0059] Once the liquid reaches the outer edge 21 of the disc 20, it may collect at the edge, and then eventually separate from the edge 21 as particles or droplets.

[0060] Once separated, the particles of liquid will fly outwardly through the surrounding atmosphere in the chamber 14 towards the chamber walls 34, 36. During this flight, the particles will interact with gas fed into the chamber 14 using the gas inlet 44 (e.g. carbon dioxide). In some example, the gas may be continuously fed into the chamber 14. In other examples, the gas may be intermittently fed into the chamber 14. [0061] Generally, the liquid particles are sufficiently small that the gas will rapidly dissolve into them and approach equilibrium saturation during the flight time of the particles (e.g. between disengaging from the spinning disc 20 and contacting the walls 34, 36 of the chamber 14). In some examples, the flight time is less than 100 milliseconds. In yet other examples, the flight time is less than 50 milliseconds.

[0062] To accomplish the required mass transfer within the brief flight times of the droplets, the droplets should be extremely small and be of exact or very similar droplet sizes, or at least be almost entirely and reliably below a critical droplet size, so as to closely approach equilibrium with the surrounding gas. For example, in some examples, the droplets should be less than 100 microns in diameter. In other examples, the droplets should be less than 60 microns in diameter.

[0063] Furthermore, the distance between the edge 21 of the spinning disc 20 and the walls 34, 26 of the chamber 14 should be selected to allow the droplets to closely approach saturation with the surrounding gas prior to being arrested against the walls 34, 36. Accordingly, the chamber 14 should have a chamber diameter C sufficiently larger than disc diameter D such that the droplets have an extended life within the atmosphere prior to their coalescence into larger droplets or against a surface of the chamber walls 34, 36.

[0064] Generally, the chamber diameter C will be selected such that the droplets will tend to come to rest within the atmosphere before contacting the chamber walls 34, 36. Thus, the particles will have an extended life within the gas prior to coalescence so as to obtain a desired equilibrium level.

[0065] However, in some cases, the chamber diameter C may be sufficiently small so that the droplets tend to reach the walls 34, 36 before being arrested by the atmosphere in the chamber 14, thus coalescing on the walls 34, 36. [0066] Once arrested within the atmosphere (or on the walls 34, 36), the gas-liquid droplets will tend to collect and/or grow and will eventually fall into the lower tank head 18, where they can be subsequently extracted via the outlet fitting 63. In this manner, the apparatus 10 can be used to provide for mass transfer of gases into liquids.

[0067] Generally, the following equation can be used to estimate the diameter of water droplets produced by the spinning disc 20:

[0068] d = 4/[Ω(Dp/σ)^1/2] (1)

[0069] where d is the droplet diameter in centimeters, Ω is the rate of rotation of the disc 20 in revolutions per minute (RPM), D is the disc diameter in centimeters, p is the density of the liquid medium being dispersed as droplets, and σ is the surface tension of the liquid medium.

[0070] In some cases, where the liquid does not perfectly wet the spinning disc 20, this equation should be corrected by dividing the answer by cos(Φ), where Φ is the wetting contact angle. For example, water often does not have a wetting reaction with metal surfaces (e.g. a metal spinning disc 20). Accordingly, in some examples such surfaces may be chemically or physically modified (e.g. using a coating) to provide hydrophilic surfaces, where cos(Φ) is roughly equal to unity.

[0071] It has been found that the roughly monodisperse droplets produced by the spinning disc 20 travel a given fixed distance in the surrounding gaseous medium (based on the operating conditions of the apparatus 10) before their velocity declines to essentially the ambient drag velocity within the gas. The result is a cloud of droplets accumulating in a dense and stationary ring at a generally fixed distance from the spinning disc 20. This fixed distance generally follows the form:

[0072] X/d = P (2)

[0073] where X is the distance the primary droplet travels from the spinning disc in centimeters before the droplet loses their kinetic energy and come roughly to rest, and P is a constant that may be determined by observation. For example, for water droplets released into air at ambient pressure, P is equal to 2540.

[0074] Substituting equation (1) into (2), and adding a term to account for the viscosity of a surrounding atmosphere in the chamber 14 (e.g. carbon dioxide) under pressure as compared with ambient air, the following equation may be obtained to solve for the distance X:

[0075] X = 10,100 /[Ω(Dp/σ)^1/2] ^* (η_aιr / η_co2) (3)

[0076] The ratio of viscosities for air (171 micro Poise) and carbon dioxide (139 micro Poise) is approximately 1.23, and this is roughly independent of the surrounding gas pressure. The surface tension of water is approximately 72 dynes/cm, and the density of water is 1.00 grams/cm³, all at a temperature of approximately 4°C.

[0077] In some embodiments, the maximum flow rate, Q_max of liquid that can be fed onto the spinning disc 20 is limited by the volume that would "flood" the surface and inhibit the formation of small droplets. This maximum flow rate is roughly equal to:

[0078] Q_max = π² D²Ωd = ( 4π² D²) / (Dp/σ)^1/2 (4)

[0079] EXAMPLE 1 : Calculated Droplet Size and Distance of

Droplet Projected From An Apparatus Operating as a Carbonator.

[0080] According to one example, the apparatus 10 was configured with the spinning disc 20 having a disc diameter D of 10 cm, and using an AC synchronous motor to drive the drive mechanism 60.

[0081] When operating such an apparatus 10 with the disc 20 rotating at 3600 RPM, a carbon dioxide atmosphere with an absolute pressure of 45 psi (roughly 3 atmospheres) within the chamber 14, and water as the liquid, droplets of 0.00298 cm (roughly 30 micron) can be produced. Under these conditions, droplets of this size tend to be thrown a distance of approximately 9.2 cm from the edge 21 of the disc 20 prior to being arrested by their friction within the surrounding gas. [0082] Accordingly, the chamber diameter C should be made larger than 28.4 cm to enhance the contact time between droplets or particles and the surrounding atmosphere in the chamber 14 and provide for improved dispersion of the carbon dioxide into the water. After coalescing, the gas-liquid mixture can be collected in the bottom tank head 18, and subsequently extracted.

[0083] Alternatively, the chamber diameter C may be selected to be less than 28.4 cm if it is desired that the liquid droplets impact the walls 34, 36 of the chamber 14 rather than become entrained within the surrounding atmosphere.

[0084] The roughly 30 micron droplets produced by the spinning disc

20 in this example will tend to achieve approximately 97% equilibrium with the surrounding carbon dioxide atmosphere in approximately 0.05 seconds after leaving the edge 21 of the disc 20. However, because of time spent by the liquid spreading upon the surface of the disc 20 (prior to separation from the edge 21), the actual equilibrium results are generally better than is predicted by the diffusion into droplets alone.

[0085] If the walls 34, 36 of the chamber 14 in this example are selected to be larger than the specified 28.4 cm, then the droplets produced by the spinning disc 20 will tend to accumulate within a dense cloud at this distance, and will have much greater residence time within the gas atmosphere of the chamber 14 prior to coalescing into larger droplets.

[0086] The maximum recommended flow rate (Q_maχ, calculated using equation (4) above) for this particular example is approximately ten liters of liquid per minute. It can be seen by inspection of equation (4) that the maximum flow rate of the apparatus 10 can be improved by increasing the size of the disc 20, and not through an increase in the speed of rotation of the disc 20. The system can be operated above the Q_max value, but generally only in cases where mass transfer is favored, such as in carbonation. [0087] In some examples, a rotating capillary may be used in an apparatus instead of the spinning disc 20. For example, illustrated in Figure 4 is a rotor assembly 90 for use with an apparatus according to another embodiment of the invention.

[0088] The rotor assembly 90 generally includes one or more surfaces sized and shaped so as to define at least one capillary, and is configured to be rotated at an angular velocity selected such that liquid received in an inner region will adopt an unsaturated condition on each surface (as the liquid moves outwardly) such that the liquid flows as a film along the at least one surface and does not continuously span the capillary. Upon reaching the edge of the capillary, the liquid separates to form particles or droplets.

[0089] As shown, the rotor assembly 90 typically includes a set of circular plates (e.g. an upper plate 92 and a lower plate 94) spinning together on a hub or spindle 96. The upper and lower plates 92, 94 are spaced apart by a gap distance "d" and generally define the capillary therebetween.

[0090] In this embodiment, the liquid is provided into an inner region 97 of the rotor assembly 90 using a feed tube 98. The liquid is then allowed to flow into the capillary (e.g. between the two plates 92, 94, in some cases via apertures 99 in the feed tube 98). As the rotor assembly 90 rotates, the liquid moves outwardly between the plates 92, 94, reaching the edges 93, 95 of the plates and eventually separating from the edges 93, 95 as particles (e.g. fine ligaments, droplets or fibers, depending upon the properties of the liquid and the operating conditions of the rotor assembly 90).

[0091] In some examples, the liquid may transition from saturated flow

(e.g. flow that spans the gap width d) to unsaturated flow (e.g. flow that does not span the gap width but which exists as thin films) within the capillary and before separating from the edges 93, 95. In an unsaturated condition, the liquid does not span the entire gap width, but rather exists as separate thin films on the surfaces of each of the upper plate 92 and lower plate 94, as urged by the increasing centripetal force as the liquid moves toward the outer edges 93, 95 of the plates 92, 94. [0092] The use of such a spinning rotor assembly 90 tends to allow roughly double the flow rates, since two surfaces are being used for the release of the droplets.

[0093] In some examples, the rotor assembly 90 may be provided and operated within a tank 12 in a manner similar to that of the disc 20 as described above.

[0094] In some examples, the two plates 92, 94 may be coated with a hydrophilic medium or other coating to facilitate a transition from saturated flow within the capillary to unsaturated flow.

[0095] In some examples, as shown in Figure 4, the edges 93, 95 of the plates 92, 94 may be sharp edges having a radius selected so to inhibit the accumulation of liquid thereon.

[0096] In other examples, the edges 93, 95 may be blunt edges. In yet other examples, each of the edges 93, 95 may be bifurcated (e.g. the edges 93, 95 may be V-shaped or U-shaped) so as to provide an upper edge and lower edge on each of the edges 93, 95.

[0097] In some examples, three or more plates may be stacked together in an array in a rotor assembly. For example, the rotor assembly 90 may be modified by providing one or more intermediate rotor plates between the upper plate 92 and lower plate 94. These intermediate rotor plates will cooperate with the upper and lower plates 92, 94 so as to define capillaries between each pair of opposing surfaces. The intermediate plates may have sharp edges, blunt edges, bifurcated edges, or any combination thereof.

[0098] Further details on the rotor assemblies that may be used are described in the PCT Patent Application entitled "Apparatus, Systems and Methods for Producing Particles Using Rotating Capillaries", filed on March 16, 2009 in the Canadian Intellectual Property Office, the entire contents of which are hereby incorporated by reference. [0099] According to some of the embodiments described herein, it is possible to achieve exceptionally high performance mass transfer of gases (e.g. carbon dioxide) into liquids (e.g. water).

[00100] Generally, the apparatus, systems and methods described can be used within very small or very large-scale applications, especially when such gas transfer is accomplished at elevated pressures and where the uniformity and proportion of gas transferred to each unit of liquid must be exceptionally precise.

[00101] For example, if the liquid reaches greater than 95% of equilibrium with the surrounding gas atmosphere in less than 50 msec, then the apparatus as described herein might be considered to be a "near perfect" mass transfer device, where liquid always emerges at the desired gas saturation regardless of the actual residence time.

[00102] The apparatus and methods can be used in applications where the mass-transfer process might support chemical or biological processes, or for use in producing carbonated liquids. Some examples include oxygen transfer to support fermentation, aerobic digestion, gas-liquid chemical engineering processes or three-phase processes (e.g. where a solid is dispersed in a liquid that contains a dispersed or dissolved gas).

[00103] One typical case is carbonation, where it is desirable to transfer a precise volume of carbon dioxide gas into a precise quantity of water. Excessive carbonation at elevated pressure tends to result in undesirable foaming or "flashing" of carbonated drinks dispensed through a nozzle (as in post-mix applications). Alternatively, inadequate carbonation results in a "flat tasting" drink.

[00104] Failure to obtain optimal carbonation is said to be the single most common and pervasive source of quality control problems in carbonated beverage production in post-mix systems, even more common than problems with syrup blending (e.g. Brix control). [00105] By using the various embodiments described herein, it is possible to accomplish a precise transfer of gas into a liquid without complexity or recourse to complex sensors, feedback loops, or controls. Instead, it is achieved through nearly instantaneous accomplishment of the desired equilibrium using physics and mass-transfer principles.

[00106] While the above description provides examples of one or more methods and/or apparatuses, it will be appreciated that other methods and/or apparatuses may be within the scope of the present description as interpreted by one of skill in the art.

Claims

1. An apparatus for mass transfer of a gas into a liquid, comprising: a. a tank that defines a chamber for receiving the gas; and b. at least one surface provided within the chamber, each surface having an inner region, an outer region and an edge adjacent the outer region; c. wherein each surface is configured to receive the liquid at the inner region and rotate such that the liquid flows on the surface from the inner region to the outer region, and, upon reaching the edge of the surface, separates to form liquid particles that move outwardly through the gas in the chamber; d. and wherein the liquid particles are sized so that the gas is absorbed by the liquid particles to produce a mixed liquid saturated with the gas during a brief flight time of the liquid particles through the chamber.

2. The apparatus of claim 1 , wherein at least a substantial portion of the liquid particles have a size less than a critical characteristic diffusion length so as to encourage the gas in the chamber to diffuse therein during the flight time of the particles through the chamber.

3. The apparatus of claim 1 , wherein at least a substantial portion of the liquid particles have a size less than 60 microns.

4. The apparatus of claim 1 , wherein the flow rate of liquid being provided to the inner region is less than a maximum flow rate calculated to flood each surface and inhibit the formation of liquid particles.

5. The apparatus of claim 1 , wherein the chamber is sized such that the liquid particles separating from the edge of each surface have an extended life within the gas prior to coalescence so as to obtain a desired equilibrium level.

6. The apparatus of claim 5, wherein the chamber is sized such that the particles are slowed by the gas and tend to come to rest within the chamber prior to contacting the outer walls of the chamber.

7. The apparatus of claim 5, wherein the liquid particles are almost entirely below a critical size and the chamber is sized such that the liquid particles closely approach equilibrium before coalescing on outer walls of the chamber.

8. The apparatus of claim 1 , wherein the at least one surface includes a generally flat disc.

9. The apparatus of claim 1 , wherein the liquid is smoothly fed to the inner region of each surface so as to inhibit the formation of droplets of poly- disperse sizes.

10. The apparatus of claim 8, further comprising an inlet spout for providing the liquid to the inner region of each disc.

11.The apparatus of claim 10, wherein the inlet spout has a lower end portion provided adjacent to the disc such that the liquid may be smoothly fed to the inner region of each disc so as to inhibit the formation of droplets of poly-disperse sizes.

12. The apparatus of claim 8 wherein the disc is a metal disc.

13. The apparatus of claim 12, wherein the surface of the metal disc is modified to provide a hydrophilic surface.

14. The apparatus of claim 1 , wherein the at least one surface includes a rotor assembly having at least one capillary.

15. The apparatus of claim 14, wherein rotor assembly may be rotated at a speed selected so that the liquid adopts an unsaturated condition on each surface as the liquid moves outwardly from the inner region wherein the liquid does not continuously span the capillary.

16.A carbonator for mass transfer of carbon dioxide into water, comprising: a. a tank that defines a chamber for receiving the carbon dioxide; and b. at least one surface provided within the chamber, each surface having an inner region, an outer region and an edge adjacent the outer region; c. wherein each surface is configured to receive the water at the inner region and rotate such that the water flows on the surface from the inner region to the outer region, and, upon reaching the edge of the surface, separates to form water particles that move outwardly through the carbon dioxide in the chamber; d. and wherein the water particles are sized so that the carbon dioxide is absorbed by the water particles to produce a carbonated water saturated with the carbon dioxide during a brief flight time of the water particles through the chamber.

17. The carbonator of claim 16, wherein at least a substantial portion of the water particles have a size less than a critical characteristic diffusion length so as to encourage the carbon dioxide in the chamber to diffuse therein during the flight time of the particles through the chamber.

18. The carbonator of claim 16, wherein at least a substantial portion of the water particles have a size less than 44 microns.

19. The carbonator of claim 16, wherein the flow rate of water being provided to the inner region is less than a maximum flow rate calculated to flood each surface and inhibit the formation of water particles.

20. The carbonator of claim 16, wherein the chamber is sized such that the water particles separating from the edge of each surface have an extended life within the carbon dioxide prior to coalescence so as to obtain a desired equilibrium level.

21. The carbonator of claim 20, wherein the chamber is sized such that the particles are slowed by the carbon dioxide and tend to come to rest within the chamber prior to contacting the outer walls of the chamber.

22. The carbonator of claim 20, wherein the water particles are almost entirely below a critical size and the chamber is sized such that the water particles closely approach equilibrium before coalescing on outer walls of the chamber.

23. The carbonator of claim 16, wherein the at least one surface includes a generally flat disc.

24. The carbonator of claim 16, wherein the water is smoothly fed to the inner region of each surface so as to inhibit the formation of droplets of poly- disperse sizes.

25. The carbonator of claim 23, further comprising an inlet spout for providing the water to the inner region of each disc.

26. The carbonator of claim 25, wherein the inlet spout has a lower end portion provided adjacent to the disc such that the water may be smoothly fed to the inner region of each disc so as to inhibit the formation of droplets of poly-disperse sizes.

27. The carbonator of claim 23 wherein the disc is a metal disc.

28. The carbonator of claim 27, wherein the surface of the metal disc is modified to provide a hydrophilic surface.

29. The carbonator of claim 16, wherein the at least one surface includes a rotor assembly having at least one capillary.

30. The carbonator of claim 29, wherein rotor assembly may be rotated at a speed selected so that the water adopts an unsaturated condition on each surface as the water moves outwardly from the inner region wherein the water does not continuously span the capillary.

31.A method for mass transfer of a gas into a liquid, comprising the steps of: a. providing a chamber having the gas therein; b. providing at least one surface within the chamber, each surface having an inner region, an outer region and an edge adjacent the outer region; c. providing a liquid to the inner region of each surface; and d. rotating the surface at an angular velocity selected such that the liquid will move from the inner region to the outer region, and, upon reaching the edge, separates from the at least one surface to form at least one liquid particle that moves outwardly through the gas; e. wherein the liquid particles are sized so that the gas is absorbed by the liquid particles to produce a mixed liquid saturated with the gas during a brief flight time of the liquid particles through the chamber.

32. The method of claim 31 , wherein at least a substantial portion of the liquid particles have a size less than a critical characteristic diffusion length so as to encourage the gas in the chamber to diffuse therein during the flight time of the particles through the chamber.

33. The method of claim 32, wherein at least a substantial portion of the liquid particles have a size less than 60 microns.

34. The method of claim 31 , wherein the flow rate of liquid provided to the inner region is less than a maximum flow rate calculated to flood the surfaces and inhibit the formation of liquid particles.

35. The method of claim 31 , wherein the liquid is smoothly fed to the inner region of each surface so as to inhibit the formation of droplets of poly- disperse sizes.

36. The method of claim 31 , wherein the liquid particles are sized so that the gas is absorbed by the liquid particles in less than 100 milliseconds.

37. The method of claim 31 , wherein the gas is provided in the chamber at a pressure greater than atmospheric pressure.

38. The method of claim 31 , wherein the chamber is sized such that the liquid particles separating from the edge of each surface have an extended life within the gas prior to coalescence so as to obtain a desired equilibrium level.

39. The method of claim 38, wherein the chamber is sized such that the particles are slowed by the gas and tend to come to rest within the chamber prior to contacting the outer walls of the chamber.

40. The method of claim 38, wherein the liquid particles are almost entirely below a critical size and the chamber is sized such that the liquid particles closely approach equilibrium before coalescing on outer walls of the chamber.

41. The method of claim 31 , wherein the gas includes carbon dioxide and the liquid includes water, and the mixed liquid includes carbonated water.

42. The method of claim 31 , wherein the mixed liquid supports a biological reaction.

43. The method of claim 31 , wherein the mixed liquid supports a chemical reaction.

44. The method of claim 31 , wherein the gas includes oxygen and the method is used to encourage fermentation.

45. The method of claim 31 , wherein the mixed liquid encourages aerobic digestion.

46. The method of claim 31 , further comprising dispersing solid particles in the liquid before forming the liquid particles.